Observables in quantum mechanics are conventionally required to be Hermitian to ensure that measured values are real numbers, which is critical for the validity of Born's rule. This requirement arises from historical postulates and the mathematical framework of quantum mechanics, particularly the use of complex Hilbert spaces and probability distributions. While Hermitian operators are commonly used due to their properties, it is noted that they are not strictly necessary for all observables, as other mathematical constructs like Positive Operator Valued Measures (POVMs) can also be employed. The discussion emphasizes that the focus should be on maintaining a self-consistent probability calculus rather than strictly adhering to the historical conventions of Hermitian operators. Ultimately, the effectiveness of the mathematical formalism in predicting experimental outcomes is what underpins these conventions.